1. Field of the Invention
This invention relates to offshore drilling platforms, and in particular to devices for guiding and positioning risers of such drilling platforms.
2. Description of the Prior Art
In an offshore oil or gas well a riser is connected between the subsea wellhead and the drilling platform. Oftentimes the subsea wellhead is not in exact alignment with the drilling platform that is used to secure the riser or handle the riser during assembly. Further, the drilling platform may be subject to movement from wave action and the like, while the riser is stationarily held at the wellhead.
It is important that the portion of the riser string near the platform be in generally vertical alignment with the platform. Without this, it may be difficult to conduct drilling operations or assemble the riser or drilling strings at the surface where string sections must be aligned and coupled together. Centralizing devices are therefore used to maintain the riser in a vertical orientation at the platform. Because of movement between the wellhead and the platform, due to wave action and the like, the centralizer must allow some relative movement between the riser and the platform while maintaining the proper orientation of the riser.
Another function of the drilling riser centralizer is to keep the riser centralized when raising or lowering the risers to prevent the riser flanges from striking and damaging associated equipment.
While there are devices available to accomplish these objectives, improvements are needed.